(1) Field of the Invention
This invention relates to heat transfer printing fabrics with dispersed dyestuffs.
(2) Description of the Prior Art
Transfer printing is conducted primarily on 100% polyester knit fabric. The process is conducive to use on poylester fabric because polyester softens in the temperature range necessary for sublimation of disperse dyestuffs. Dye classes with ionic character are not readily sublimable; therefore, their use in transfer printing is restricted.
Because of the affinity of polyester fibers for disperse dyes, cotton-polyester blend fabrics have been used for transfer printing; however, because cotton has very little affinity for disperse dyes, treatment of the fabric prior to printing is necessary to obtain adequate color brightness and depth of shade.
Several methods for polymer modification of cotton-polyester fabric for transfer printing are available, but those that are relevant consist of the application of preformed polymers to the fabric, or other surface treatments, as in British Pat. No. 1,501,889. Such surface effects generally stiffen the fabric, thereby giving it a harsh hand. In addition, the mositure absorption capacity of the fabric is severely reduced, negating the beneficial effects of the cotton component of the blend.
The unique nature of the disperse dyestuffs is that they are readily sublimable when heated at temperatures in the vicinity of 200.degree. C. and higher. This characteristic allows the dyes to be transferred at elevated temperatures from the dye-printed paper to the desired fabric. If the fabric is composed of 100% polyester, color saturation after printing is excellent; however, if the fabric contains a substantial amount of cotton cellulose (in excess of 20%), color brightness upon printing is markedly reduced. Moreover, color saturation is further reduced upon laundering as dye is removed from the low affinity cotton component of the fabric. To improve dye affinity of the cotton component of the fabric, the fabric must be treated with a disperse dye solvent, such as glycol, or some substance that can be attached to the cellulose. Such a treatment will allow the cellulosic fiber component to have increased affinity for the disperse dye. The negative aspects of these treatments are compounded as the percentage of the cotton component increases. As the percentage of polyester is reduced, more additive has to be added to the fabric to compensate for the low affinity of cellulose for disperse dyes. In the case where preformed polymeric material is deposited on the fabric surface, the net result is a fabric with a rather harsh or stiff hand and low hydrophilic properties. In the case where high concentrations of dye solvent are employed, such as polyethylene glycol or similar agents, increased amounts of cellulosic crosslinking agent, such as dimethylol dihydroxyethyleneurea or methylolated melamine, is needed to insolubilize the glycol. This causes fabric strength properties to be reduced if too much crosslinking is used and gives the fabric durable-press properties even though they may not be desired. Furthermore, dye solvents, such as glycols can cause dye migration problems. Other processes, such as acetylation and benzoylation, are suitable for modifying cellulose to improve heat transfer printing, but these reactions do not result in the formation of polymers.